How to Manage Pests

Mosquitoes

Managing Mosquitoes on the Farm Section 6: Managing Stagnant Waters Created by Agricultural Activities Published 2005 Sections of this publication:

Why You Should Care About Mosquito Control West Nile Virus You May Be Raising the Mosquito That Is Biting You! Mosquito Prevention Three Basic Principles of Mosquito Prevention Natural Waters Associated With Farms Managing Stagnant Waters Created by Agricultural Activities Irrigated Fields for Upland Crops Mosquito-Free Irrigated Pastures Rice Dairy Operations Biological and Chemical Mosquito Control Common Mosquitoes and Their Life Cycles Acknowledgments For More Information

Impoundments

Impounded water can be a source of mosquitoes, but a few simple approaches will help reduce mosquito breeding sites. For example, a reservoir will not produce mosquitoes if its sides and bottom are properly graded, there is little emergent vegetation, and it is stocked with insect-eating fish. In general, a steep-sided pond of at least 3 feet (1 m) in depth (to cover bottom-growing weeds) offers the least problem. Destroy weeds around the margin of the pond to help eliminate hiding places for larvae. Maintain a stable water level to minimize the area where floodwater mosquitoes can lay their eggs. Equip water sources with float valves to maintain the water level.

Miscellaneous Breeding Habitats

Many items create areas where mosquitoes can breed: leaky irrigation piping, old tires, birdbaths, tarps that form puddles, clogged gutters, paint cans, boats or wheelbarrows stored upright, open garbage cans and lids, and pet food bowls. Inspect your property and fix, clean up, invert, puncture, or regularly flush out any of these potential problem areas. Because they typically contain few or no predators, each of these small habitats can produce hundreds of biting mosquitoes.

Poorly Maintained Cesspools and Septic Tanks

Septic systems can produce droves of mosquitoes. A properly constructed and maintained cesspool or septic tank should have an adequate soakage pit, cover, vent, and overflow outlet. Check your local health department requirements.

Road Ruts and Potholes

Even relatively small road ruts and potholes can produce mosquitoes if water stands in them during in warmer weather, because these waters contain few predators.

Treeholes

Rain water that accumulates in treeholes can provide an ideal place for the western treehole mosquito to develop its larvae, usually in winter and spring. This mosquito carries dog heartworm, and dogs should be protected against this serious disease. Treeholes can occur in old orchard and landscape trees as well as in wild trees. Holes may be caused by rot, fire injury, or from pruning that leaves a hollow at the center of the tree. Fill treeholes with cement or other substances. Keep in mind that treeholes may provide bird nesting habitat during the drier months; it may be preferable to drill drains from the base of the treehole to the outside and remove debris that clogs the holes. Consult an arborist about treeholes in valuable or potentially hazardous trees. Methoprene pellets added to holes prevent mosquitoes from maturing (see the section Chemical Control); add these before the holes fill or anytime before the mosquitoes pupate and renew them annually.

Livestock Watering Ponds

Ponds and natural pools that livestock drink from may become serious mosquito-breeding areas. Animal waste adds nutrients to the water that benefit mosquitoes, and hoofprints create puddles where mosquitoes may be isolated from predators. If feasible, fence ponds along the edge to create a single access area. This keeps the animals from trampling the entire edge, although if too much room is left between the pond and fence, animals may still create ruts. Paving the access point can reduce puddles, but be sure to provide good footing for the animals. Weed control reduces hiding places for mosquitoes. It may be necessary to treat these ponds regularly with a biological larvicide or to introduce insect-eating fish if they are not already present. However, do not introduce fish unless the pond is man-made and isolated from natural waters.

Watering Troughs

Troughs and other containers that provide water for animals can easily become a source of mosquitoes. The ground surface around the troughs often becomes roughened by animal hooves, producing hundreds of small water pockets. Permanently correct this potential source of mosquitoes by providing drainage or paving the area. Temporary improvement can be had by flushing out the water every week if drainage outside the trough area is good, or by treating the water with a biological larvicide. Do not add chemical insecticide to water that livestock may drink. Clean cattle tanks and watering troughs regularly to prevent mosquitoes from multiplying. Mosquitofish may also be added to provide control. Remove or destroy troughs or tanks that are not in active use.

Managing Mosquitoes on the Farm, UC ANR Publication 8158 Sharon P. Lawler and Gregory C. Lanzaro, Department of Entomology, University of California, Davis

Copyright © 2005 The Regents of the University of California, Division of Agriculture and Natural Resources. All rights reserved.